A group of thirteen investigators request funds for an Aviv 62 DS CD spectrometer to replace a similar instrument which was recently moved to New York University by Dr. Neville Kallenbach. The instrument is essential to the PHS funded research programs of these investigators. Its availability must also benefit the scientific community at the University of Pennsylvania in general including potential users not yet identified by the P.I. since the loss of the Kallenbach CD spectrometer left this university without any such instrumentation; the nearest CD spectrometer being at Swarthmore College about 20 miles away. The use of the CD instrument requested by the projects described in this proposal fall into several broad areas. The first is to screen small (less than 30 residues) native peptides for incipient secondary structure formation. Peptides identified in this way can then be subjected to rigorous structural analysis by the high resolution techniques provided by NMR. This will be a major use for many of the investigators (Roder, Englander, Opella, LU and Johnson). Synthetic peptides which have been engineered to adopt secondary structure will also be investigated (Paterson and Williams). Other investigators wish to use CD to screen for structural changes in proteins of known structure which might result from sit directed mutagenesis of the primary sequence (Paterson, Cooperman, Karush, Roder, Rubin). Changes of conformation invoked by changing the molecular environmnent of proteins will also be measured by CD (Roder, Englander, Johnson and Opella). Finally for many proteins which have not yet been crystallized and are too large for NMR structural analysis, CD provides the only tool for conformational analysis (Cooperman, Golub, Jaffe, Rubin and Johnson). The CD spectrometer requested will be located in the Johnson Pavilion in the laboratory space of Dr. Robert Johnson. This location is convenient for all of the investigators since eight of the investigators have laboratories in the Johnson Pavilion or in buildings contiguous with it and the Johnson Pavilion is located centrally between the Dental Medicine and Chemistry buildings which house the other five investigators.